1. Field of the Invention
The present invention relates to an ink-jet printer and a control method thereof, and more particularly, to an ink-jet printer which can be operated by power supply from, e.g., either a rechargeable secondary battery or a power supply unit of converting a commercial power source into a DC power source, acting as an operation power source, and a power control method thereof.
2. Related Background Art
In recent years, various electronic apparatuses such as a portable personal computer, a portable telephone, a video camera, a portable printer and the like have appeared on the market.
These electronic apparatuses are downsized in consideration of portability, and can be used in a state, i.e., a cordless state, being not connected to a household power source.
Therefore, each of these electronic apparatuses is constituted to be able to be used without connecting it to the household AC power source through a power cord, in such a way that a battery is built into the electronic apparatus or a unit such as a battery pack having a battery built-in is externally connected to the electronic apparatus.
As the power source to be used for these electronic apparatuses, a rechargeable battery, i.e., a so-called secondary battery, is frequently used. Here, as the secondary batteries, a nickel-cadmium battery, a nickel-hydrogen battery, a lithium-ion battery and the like are known.
On one hand, an external power supply unit (generally called an AC adapter) of converting the AC power source into a DC power source can be connected to the electronic apparatus so that it can be operated also based on the AC power source in a house, an office or the like. Also, a current to charge the secondary battery is supplied from the AC adapter.
The secondary battery is generally charged in a case where the AC power source connected to the electronic apparatus is turned on and the electronic apparatus has electric power in reserve because it does not perform high-current driving such as a mechanical operation or the like, or in a case where the electronic apparatus is in a power-off state.
Therefore, even while the electronic apparatus is not powered, if the AC adapter is being connected to the electronic apparatus, it is necessary to be able to automatically charge the secondary battery without any user's operation.
For this reason, in the case where the above electronic apparatus is not powered, the structure to shut off the power from the AC power source to the AC adapter by a mechanical switch is not adopted generally. Instead, even when the electronic apparatus is not powered, the power is supplied to the electronic apparatus to operate a built-in MPU (microprocessor unit), whereby on and off states of the power switch of the electronic apparatus are always detected.
In such a structure, to decrease power consumption while the power switch is turned off, generally, clock frequencies of the MPU and a control circuit for controlling the electronic apparatus are decreased as compared with the case where the power switch is turned on, or the clock frequencies are stopped.
However, in the above conventional case, although the lower consumption as above is achieved, it is still necessary to supply the power to a logic circuit including the MPU of the electronic apparatus, whereby it is not avoided that the electronic apparatus consumes the electric power more than a certain value.
Moreover, the AC adapter consumes the electric power of about 0.3 W to 0.5 W even in an unloaded state that the electronic apparatus is not powered, and the power consumption tends to increase with accelerating speed if the electronic apparatus performs some operation.
Therefore, in order to suppress the power consumption to about 0.5 W and below in the state that an overall system including the AC adapter and the electronic apparatus is not powered, it is necessary to set the power consumption of the electronic apparatus to substantially “0” while it is not powered. If it pays attention to the current state that reactive power while the electronic apparatus is not powered becomes a problem due to recent concern about energy saving and tighter regulations, it is demanded to further decrease the power consumption.